Yesterday, as part of a panel on machine consciousness, I saw Jack Copeland deliver a razor-sharp talk based on a paper that he published last year with Douglas Campbell and Zhuo-Ran Deng, entitled “The Inconceivable Popularity of Conceivability Arguments“. To give you an idea of what the paper is about, I reproduce the abstract here:
Famous examples of conceivability arguments include: (i) Descartes’ argument for mind-body dualism; (ii) Kripke’s ‘modal argument’ against psychophysical identity theory; (iii) Chalmers’ ‘zombie argument’ against materialism; and (iv) modal versions of the ontological argument for theism. In this paper we show that for any such conceivability argument, C, there is a corresponding ‘mirror argument’, M. M is deductively valid and has a conclusion that contradicts C’s conclusion. Hence a proponent of C—henceforth, a ‘conceivabilist’—can be warranted in holding that C’s premises are conjointly true only if she can find fault with one of M’s premises. But M’s premises—of which there are just two—are modeled on a pair of C’s premises. The same reasoning that supports the latter supports the former. For this reason a conceivabilist can repudiate M’s premises only on pain of severely undermining C’s premises. We conclude on this basis that all conceivability arguments, including each of (i)—(iv), are fallacious.
It’s a great paper, but I’m not sure the mirroring move against Descartes works, at least not as it is expressed in the paper. Although the text I quote below is from the paper, I composed this objection while listening to (and recalling) the talk. I apologise if the paper itself, which I have not read carefully to the end, blocks or anticipates the move I make here (please let me know if it does).
“I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my understanding of it. Hence the fact that I can clearly and distinctly understand one thing apart from another is enough to make me certain that the two things are distinct, since they are capable of being separated, at least by God… [O]n the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of a body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I am really distinct from my body, and can exist without it.”(Cottingham, Stoothoff, & Murdoch, 1629, p. 54)
“Setting φ, ψ, and μ as follows:φ: Mind=Bodyψ: Mind≠Bodyμ: □(Mind≠Body),we get:D1.⬦c(Mind≠Body)D2.⬦c(Mind≠Body)→⬦(Mind≠Body)D3.⬦(Mind≠Body)→□(Mind≠Body)D4.⬦(Mind=Body)→¬□(Mind≠Body)____________________D5. ¬⬦(Mind=Body)Here Descartes uses a (theistic) version of CEP to infer that it is possible for mind and body to be distinct. From this he infers they are actually distinct. Why does he think he can make this move from mere possibility to actuality? Presumably because he is assuming D3, or something like it, as a tacit premise (Robinson, 2012).”